Motor speed control device

ABSTRACT

A system for controlling the speed of a direct current motor. The system employs a pair of breaker points for opening and closing the circuit containing the motor. By varying the frequency of contact between the breaker points and the period of time the points are in contact, different pulsations of current are transmitted to the motor to regulate its speed.

This application is a continuation of application Ser. No. 130,603,filed Apr. 2, 1971, which is a division of application Ser. No. 769,177,filed Oct. 21, 1968, and now U.S. Pat. No. 3,581,177.

BACKGROUND OF INVENTION

As indicated, the invention is particularly useful in controlling thespeed of a direct current motor. Many systems presently employed,utilize electrical devices such as variable rheostats for regulating asteady flow of current to the motor being operated. In such devices,power is lost, or dissipated in heat caused by the resistance in thecircuit. Then too, the shaft of the motor rotates at relatively littletorque at low operating speeds of the motor. This is readily apparentwhen slight pressure is applied to the rotating shaft of the motor atsuch speeds.

The invention is designed to substantially eliminate the disadvantagesindicated above by utilizing what might be termed a mechanicallyoperated apparatus for sending pulsations or surges of direct electricalcurrent to the motor, rather than regulating a steady flow of current tothe motor.

Briefly stated, the invention contemplates using a pair of breakerpoints for opening and closing a circuit containing a direct currentmotor. Means are provided for varying the frequency of contact betweenthe points and the period of time the points are in contact, to regulatethe frequency and strength of the pulsations of current transmitted tothe motor. A capacitor in circuit with the motor, is charged anddischarged as the breaker points move into and out of contact. Thecapacitor, when discharging, sends the pulsations of current to themotor.

The following description of the invention will be better understood byhaving reference to the annexed drawing, wherein:

FIG. 1 is a schematic drawing showing an embodiment of the invention;

FIG. 2 is a schematic drawing showing the embodiment of FIG. 1 in a morerefined circuit;

FIG. 3 is an enlarged view of another embodiment of the invention;

FIG. 4 is a schematic drawing showing the embodiment of FIG. 3 incircuit;

FIG. 5 is a schematic drawing of a system utilized for varying relativemovement between the armature and field coil of a series wound directcurrent motor; and

FIG. 6 is an enlarged view of still another embodiment of the inventionutilizing more than one pair of breaker points.

DESCRIPTION OF THE INVENTION

Referring more particularly to FIGS. 1 and 2 of the drawing, there isshown a mechanism or device, generally indicated at 10, for controllingthe speed of a DC (direct current) motor 12. The motor speed controldevice 10 and DC motor 12 are placed in circuit 14 with a source ofdirect electrical current, e.g., battery 16, and a capacitor 18.

The motor speed control device 10 comprises a pair of contact or breakerpoints 19 and 20, which are movable relative to each other into an outof contact for opening and closing the circuit 14 to discharge andcharge the capacitor 18. As viewed in the drawing, the breaker point 20is adjustable towards and away from the other breaker point 19 which, inturn, is mechanically driven into and out of contact with the adjustablebreaker point 20.

The gap 22 between the breaker points 19 and 20, is varied by adjustingor rotating the screw 24 carrying the adjustable breaker point 20. Thescrew 24 as it rotates, moves axially through a fixed guide block 23towards the movable breaker point 19. A handle 25 is provided forconveniently rotating the screw 24.

The movable breaker point 18 is carried by a breaker arm 26, which ispivotally mounted at point A for rotation towards and away from theadjustable breaker point 20. A cam follower 28 is associated with thebreaker arm 26 and extends therefrom.

The DC motor 12 is mounted adjacent the breaker arm 26 and has arotatable shaft 30 extending therefrom. A rotor 34, provided with aplurality of cam surfaces 36, 38, 40, and 42, is coupled to the motorshaft 32 for unitary rotational movement therewith.

A spring 44, fastened to the breaker arm 26, maintains the cam follower28 in biased engaged relation against the cam surfaces 36-42 of therotor 34. Thus, the movable breaker point 19 moves in response tomovement of the cam surfaces 36-42, or rotation of the rotor 34. Itshould be appreciated from FIG. 1, that the movable breaker point 19will move into contact with the adjustable breaker point 20 four timesfor every rotation of the rotor 34.

In this particular embodiment where the rotor 34 is mounted directly onthe shaft 30 of the driven motor 12, the amplitude and frequency ofpulsations of current sent to the motor 12, are varied by a singleadjustment of the gap 22 between the breaker points 19 and 20. As seenin FIG. 2, the motor 12 can be used as a pilot motor to drive a largermotor 46 which is wired to operate in unison with the pilot motor 12.

The capacitor 18 is charged and discharges relative to the frequency ofcontact between the breaker points 19 and 20, and the period of timesaid points are in contact. Correspondingly, weaker or strongerpulsations of current are transmitted to the pilot motor 12 from thecapacitor 18 as it discharges.

FIG. 2 represents a more refined electrical circuit 14, which utilizes apair of micro-switches 50 and 52 to initially energize the circuit 14 tooperate the pilot motor 12, and bypass operation of the pilot motor 12when the larger motor 46 is operating at maximum speeds. Themicro-switch 50 is in a normally open position and the micro-switch 52is in a normally closed position. The micro-switch 50 closes when thehandle 25 is initially rotated to begin closing the gap 22 between thebreaker points 19 and 20, to place the pilot motor 12 and battery 16 inelectrical communication. Further operation of the handle 25 acts toreopen the micro-switch 50 and break the circuit. Thus, the pilot motor12 is initially activated. A rectifier 56 is provided to keep electricalcurrent in said closed circuit from passing into the larger motor 46.The micro-switch 52 will move to its open position when the motor speedcontrol device 10, is operating with the breaker points 18 and 20 incontinuous contact. This shuts down the circuit including the pilotmotor 12, and places the larger motor 46 in direct electricalcommunication with the battery 16. The reverse is true when the handle25 is rotated in the opposite direction to increase the gap 22 betweenthe breaker points 18 and 20, and bring them back to their restiveposition out of contact with each other. Another conventionally designedrectifier 54 is placed in the circuit to eliminate current feedbackthrough the pilot motor 12 and the larger motor 46.

Referring more particularly to FIGS. 3 and 4, there is shown anotherapparatus or device 60 for controlling the speed of a DC motor 62. Thisparticular system employs a pilot motor 64 which is driven at apredetermined constant rate of speed such that the breaker points willpreferably contact between 40 to 100 times per second.

The pilot motor 64 has a rotatable shaft 66 extending therefrom. A rotor68 having a plurality of cam surfaces 70, 72, and 74, is coupled to theextended motor shaft 66 for unitary rotation therewith.

A breaker arm 76 is pivotally mounted for rotation about point A', andcarries a breaker point 78. A cam follower 80 is associated with thebreaker arm 76 for riding engagement on the cam surfaces 70-74 of therotor 68. A spring 82 coacting with the breaker arm 76, is provided forholding the cam follower 80 in biased relation against the cam surfaces70-74.

An adjustable breaker point 84 is mounted for movement towards and awayfrom the movable breaker point 78 carried by the breaker arm 76. Theadjustable breaker point 84 is secured at one end 86 of a rotatable,longitudinally moving shaft 88. A handle 90 is provided at the other end92 of the rotatable shaft 88.

A pin 94 extends from the shaft 88, and is designed to ride alongintersecting surfaces 96 and 98 of a V-shaped notch 100 provided in afixed guide block 102 through which the shaft 88 extends.

A spring 104 surrounds the shaft 88 between the block 102 and handle 90,and biases the adjustable breaker point 84 away from the movable breakerpoint 78, and into its restive position where the pin 94 rests in thecrotch 105, of the V-shaped notch 100. As the handle 90 is rotated, thepin 94 travels along either sloped surface 96 or 98 to move the shaft 88longitudinally and reduce the gap 106 between the breaker points 78 and84. The adjustment of gap 106 is much faster than that disclosed in theembodiment of FIG. 1.

A dowel or lever 108 is coupled to the shaft 88 adjacent the pin 94, andextends therefrom for engaging an actuating pin 110 extending frommicro-switch 112, which is mounted adjacent the guide block 102. Thedowel 108 will move out of engagement with the actuating pin 110, as theshaft 88 moves longitudinally towards the movable breaker point 78. Thiscauses the micro-switch 112, to move to its closed position, to activatethe pilot motor 64 and solenoid contactor 122.

A micro-switch 114 is mounted adjacent the breaker arm 76, and isprovided with an actuating pin 116 for engaging the breaker arm 76 whenthe breaker points 78 and 84 are in continuous engaged relation duringmaximum speeds of the driven motor 62. The micro-switch 114 moves to itsopen position to shut down operation of the pilot motor 64. Wires orleads B and C are in electrical communication with the breaker points 84and 78, respectively, through the shaft 88 and breaker arm 76. The motorspeed controlled device 60 is placed in an electrical circuit 118 withthe driven motor 62 and a source of direct electrical current, e.g.,battery 120.

A conventionally designed solenoid contactor 122 is wired in parallelwith the pilot motor 64. When the handle 90 is rotated to close the gap106 between the breaker points 78 and 86, the micro-switch 112, moves toa closed position to complete the circuit 118. The solenoid contactor122 places the breaker points 78 and 86 in electrical communication withthe driven motor 62. The solenoid contactor 122 remains in electricalcommunication with the driven motor 62 so long as the micro-switch 112is closed. Similarly, a conventionally designed capacitor 124 is placedin the circuit 118 for charging and discharging as the breaker points 78and 84 move into and out of contact, the capacitor 124 dischargingpulsations of direct electrical current to the driven motor 62. Arectifier 126 is also utilized to keep electrical feedback from going tothe breaker points 78 and 86 and capacitor 124 from the driven motor 62.

An example of components used in the aforementioned system forcontrolling the speed of a direct current motor, is a pilot motor 64having a horsepower ranging between 1/25 and 1/35 h.p. A 12-volt battery120 can be used along with a solenoid contactor 122 having a 200-amphererating. The capacitor 124 has a rating of 5,000 microfarads at 55 volts,and the rectifier 126 has a 25 amphere rating at 200 volts.

The above equipment could be utilized to drive a motor having, forexample, two horsepower.

As previously indicated, the breaker points 78 and 84 should contactpreferably in the range of from between 40 to 100 times per second. Thedevice will operate when the breaker points 78 and 84 are making contactwithin the broader range of from 25 to 300 times per second, but not aseffectively as within the preferred range.

Also, as indicated, the pilot motor 64 is run at a constant speed toprovide the preferred range of contact between the breaker points 78 and84 as indicated above, since the pilot motor 64 in this particularembodiment is utilized only to rotate the rotor 70 and consequentlyoperate the breaker arm 76 carrying the breaker point 78.

FIG. 5 shows one means of varying the speed of the pilot motor 64 tomaintain it operating such that the breaker points 78 and 84 contactwithin the preferred range of from 40 to 100 times per second. Suchmeans are particularly useful in a series wound DC motor having anarmature 127 and field coil 128 which are movable relative to eachother. A variable resistor 129 is wired in parallel with the armature127. The minimum resistance of the variable resistor 129 should be lessthan the resistance of the armature 127. Thus, the variable resistor129, when set at a low value of resistance, acts as an electricalby-pass for current flowing through the armature 127 into the field coil128. The increased current in the field coil 128, strenthens theelectromagnetic field of the coil 128, while less current passes throughthe armature 127 to decrease its electromagnetic field. In this way, forexample, the speed of rotation of the armature 127, can be varied withina speed range such that the contact between the breaker points is withinthe preferred range indicated above. This apparatus is better than usingelectrical devices such as rheostats in series with the motor, sincethere is no loss in torque at which the motor shaft rotates. In fact,the shaft rotates at greater torque as the speed of rotation of theshaft decreases.

Referring more particularly to FIG. 6, there is shown another embodimentutilizing a plurality of pairs of breaker points. In this particularembodiment, the rotor 130 has four cam surfaces 132, 134, 136, and 138.The breaker arm 140 carries a pair of spaced breaker points 142 and 144,and has a cam follower 146 intermediate the points for riding on the camsurfaces 132-138. Springs 148 and 150 are provided for biasing the camfollower 146 against the cam surfaces 132-138.

An adjustable fork 152 carries a pair of breaker points 154 and 156 forcontacting engagement with opposing breaker points 142 aand 144,respectively. The fork 152 is provided with a single end 158 which restson a sloping or tilted cam 160 which is eccentrically disposed to thelongitudinal axis of the fork 152. The cam 160 is provided with a handle162 for rotating the cam 160. The cam 160, as it rotates, moves the fork152 axially to adjust the gap 164 and 166 between the opposing pairs ofbreaker points 142 and 154 and 144 and 156, respectively. Other devicescan be designed to accommodate any number of breaker points.

Thus, there has been provided a new and novel apparatus for controllingthe speed of a direct current motor by sending pulses of current atvarying amplitudes and frequencies to the motor. This apparatus is moremechanical in nature and does not rely on electrical devices such asvariable rheostats to control a steady flow of electrical current to themotor.

I claim:
 1. In combination:a. a first electrical circuit, including asource of direct electrical current; b. a first motor disposed in thefirst circuit and wired in series with the source therein and operableby current therefrom; c. a second electrical circuit, including a sourceof direct electrical current; d. a second motor disposed in the secondcircuit and wired in series with the source therein and operable bycurrent from the source therein when the second circuit is closed; e. aswitching mechanism wired in series with the second motor and source ofdirect electrical current in the second circuit, said mechanismincluding a pair of electrical contacts for opening and closing thecircuit; f. means for pivotally mounting the first of said pair ofelectrical contacts for reciprocating through a predetermined arc; g.means for mounting the second of said pair of electrical contacts formovement to and from the first reciprocable contact, to vary the dwellbetween said contacts; h. means coacting with the first motor forreciprocating said first contact at least twice for every rotation ofthe shaft of said first motor, said means including (I) a rotor mountedon the shaft of the first motor for unitary rotation therewith, therotor having at least two cam surfaces which are concentrically disposedabout the longitudinal axis of the shaft of the first motor, and (II) acam follower rideable on said cam surfaces for causing reciprocation ofsaid first contact into and out of engagement with the second of saidcontacts as said cam follower rides on said cam surfaces; and i. acapacitor disposed in the second circuit and wired in parallel with theswitching mechanism, such that the capacitor is charged and dischargedas the second circuit is opened and closed.
 2. The combination of claim1, wherein the second circuit is closed at a frequency in the range offrom 40 to 100 times per second.
 3. The combination of claim 1, whereinthe electrical contacts include a pair of breaker points.
 4. Thecombination of claim 3, wherein the breaker points contact at afrequency in the range of from 40 to 100 times per second.
 5. Thecombination of claim 3, which includes a rectifier for keepingelectrical feedback of the second motor from the breaker points andcapacitor.
 6. The combination of claim 3, which includes means forshutting off the first motor when the points remain in contact duringoperation of the second motor.
 7. The combination of claim 3, whereinthe first motor has an armature and field coil in series, and means areincluded for varying the electrical current passing through the fieldcoil to correspondingly vary the strength of the magnetic field of thecoil, said means being disposed in parallel electrical relation with thearmature.
 8. The combination of claim 7, wherein the means for varyingthe electrical current passing through the field coil includes avariable resistor having an electrical resistance less than theelectrical resistance of the armature.
 9. The combination of claim 1,wherein the capacitor is wired in parallel with the second motor.